adrial

In the near future (after boost gauge and Rich/Lean gauge) I'd like to get a 3" exhaust with test pipe. I am located in NY. Will I be able to pass emissions with this setup? If not, how long would it take to swap the cat for the down pipe (using jackstands...no lift)? How much HP gain would I be looking at with/without cat? The car is a '89 951 with autothority stage 2 chips & banjo bolt, but a stock intake.

Also...I just checked TurboTim's website...the price for his exhaust has gone up quite a bit...www.speedforceracing.com

$500 for 3" cat-back
$550 for 3" test pipe

Thanks in advance

Steven

I live in South Carolina. We have no automobile inspections here. I haven't a clue about the Big Apple. But, why buy a test pipe? I took mine to a local muffler shop and had my cat cut out for $40. As far as i'm concerned and from what i've read, it's the same thing. Think about it. What's a test pipe? Just a straight pipe (sort of)from the headers (if you have 'em) to the muffler. What's a pipe with the cat cut out? Just a straight pipe (sort of) from the headers (of you have 'em) to the muffler. Hope this helps. Saved me around $150. I noticed a noticeable difference right away in the power and the sound. Not a giant power increase but as I said, noticeable.

Renntag

I noticed a significant difference with the cat out.

Nevermind spending 500$. Cut the cat out as steve suggested, but leave a little bit of pipe on either end to enable flanges to be attached for reinstallation. Fab a test pipe with flanges tack-welded and bolted together at both ends, remove the test pipe and do the same thing with the cat, stick it in place with the flanges bolted allready, tack-weld the cat to the flanges. Remove, and weld 'em up. You will then have a set up that can be reverted easily for inspection purposes.

This is a worth while mod. Note: Unless you are creating over 300-350hp, you dont really need 3" exhaust. The 2 1/2" should work fine.

Good luck. Where are you in NY?

TurboTim

More often then not the biggest restriction in the stock system is the double walled piping leading to the cat! The inner tubing can collapse with age and heat cycles.I have seen it so bad... what was supposed to be round piping was U shaped! Just removing the cat might not make that big of a difference if you are blowing through 1.5" pipe(a worse case example).This is why most people buy a testpipe.The mild steel Bursch testpipes are fine.They work great.However they rust very quickly and do not have the flow capability of a 3" system.Another thing you should be aware of is that the bigger the exhaust on a turbo car, the better.


Tim
86 951 http://www.speedforceracing.com

adrial

Renntag951, I'm in upper Westchester...Where are you in NY? you have Aim? I'm AKBoost952

I think I'm just gonna cut out the cat and install a straight 2.5" pipe for now. I'll have a welding shop/exhaust place make something up for me that will let me swap the cat in/out. The car only has 68,000 miles so I'm not really worried about the problem that TurboTim mentioned. Maybe in a year or more when I'm making more power I'll be able to justify $1050 for 20hp and a better sounding car.

Thanks for the responses

spidey

im also in NY, if you are in the city there is no way (unless you know somebody..wink,wink) that the car will pass emissions with no cat. outside of the city i think its not a problem, my friend has no cat on his GTI and passes easily.

Danno

Forget the 3" exhaust, it won't do ANYTHING for you compared to a test-pipe. There's been dyno tests where a certain brand of 3" cat-back exhaust actually had less power than stock. Other systems had more high-end power but lost more in the low-end. Most of the restriction is in the middle section from the turbo downpipe through the catalytic.

For a picture of the double-wall collapse that TurboTim is talking about, check out the Lindseys' race car: http://www.ionet.net/~dlindsey/warbo...t/project.html

Typical gains from a test pipe range from 20-30hp depending upon how restricted your catalytic is and how collasped your stock double-wall tubing is. Additionaly, the forward part of the stock exhaust ahead of the cat tends to get flattened from hitting speed bumps.

TurboTim, who makes a 3" test pipe?

Macabre

What are you basing that on? I've modified exhaust systems on a couple cars and the bigger basic tube size has always had more power. 3" is not oversized for a 300+hp engine. You don't want to go too large with tubing because the gas velocity will drop too much, but the best exhaust would be none at all (as you'll find on most turbocharged race cars).

ribs

Danno...turbo tim (speedforce) and fabspeed both make 3" SS test pipes, both priced about the same. I got a 3" cat back exhaust from turbo tim, and it made a mild but noticable improvement across the rev range. (for example, with a good start from a stand still, my rear tires would never slip under full throttle in 1st gear after the clutch was completely disengauged and all wheel spin was done, but now, if I nail the throttle above 5000ish RPM's in 1st gear, the rears will break out). There is no exhaust too big (to a point) for a turbocharged cars because you don't have to worry about backpressure, exhaust gas velocity, the weird thing that keeps the gas moving quickly (harmonic resonance maybe?) etc. because it is all taken care of by the turbo. You just want what ever is leaving the turbocharger to leave quickly, therefore big is good, and bigger is better.

At least thats how I understand it.

TurboTim

I wanted to address a few things.First off..... besides the pipe before the catylitic converter being crimped real bad the pipe before the muffler is also crimped real bad(only visible once the cat-back is removed).This will effect exhaust flow! I am actually going to be dynoing some cars with a full 3" system over the stock set-up to see what kind of differences there are.

The biggest exhaust you can put on a turbo car the better.The turbo creates all the back pressure on the head that you need.Anything beyond the turbo should be as freeflowing as possible.

I make 3" stainless test pipes and actually they are almost $300 cheaper then Fabspeed.

Tim
86 951 http://www.speedforceracing.com